1. Field of the Invention
The present invention relates to an original edge detecting system, in particular, to an original edge detecting system for detecting edges of an original paper sheet. The original paper sheet is a sheet of paper, optical information to be processed provided thereon, hereinafter.
Further, the present invention also relates to an optical sensor in which a light source emits light on a to-be-detected object, and light reflected by the to-be-detected object and passing through a retroreflection path is received. Such an optical sensor may be used in the above-mentioned original edge detecting system.
2. Description of the Related Art
The Japanese Patent Publication No.59-22992 discloses an information reading apparatus in which a laser beam is directed on a rotating hologram disc, forming scan lines, to scan an information carrier. Light reflected by the information carrier is detected through a photoelectric converter, and is converted into an electric signal. Thus, information carried by the information carrier is read. In the information reading apparatus, the photoelectric converter detects light from the information carrier, which light passes a hologram used in the scanning or another hologram having a focus at a position the same as the position of the focus of the hologram used in the scanning.
The Japanese Laid-Open Patent Application No.6-242391 discloses a light-scanning original reading apparatus having light scanning means for using light for scanning a surface of an original paper sheet, the scanning light being incident on and drawing scan lines on the surface of the original paper sheet; means for detecting light reflected and diffused by the surface of the original paper sheet; and means for calculating a size and a leaning angle of the original paper sheet from information indicating intensity of the detected light and positions of the scan lines.
The Japanese Laid-Open Patent Application No.50-119537 discloses an optical reading apparatus in which light from a light source scans a to-be-read part so as to result in scanning lines on the to-be-read part, which scanning lines on the to-be-read part cross each other, and light reflected by the to-be-read part and passing a path the same as a path which the light passed when it was incident on the to-be-read part is detected. Thus, information is read from the to-be-read part.
In the above-described information reading apparatus disclosed in the Japanese Patent Publication No.59-22992, it is considered that laser light is used for the scanning. Thereby, it is possible to obtain a very small spot diameter and therefore to read information with a high resolution. However, various images may be present on the original paper sheet. Further, a paper pressing sheet which is provided in the apparatus for pressing and thus holding the original paper sheet may have dirt adhering thereon. Therefore, it may be difficult to correctly detect an edge of the original paper sheet. This is because, when a light spot of the very small spot diameter is used, it may be difficult to distinguish light intensity variation occurring when the light spot passes the edge of the original paper sheet from light intensity variation occurring when the light spot passes the various images present in the paper sheet or from light intensity variation occurring when the light spot passes the dirt adhering on the paper pressing sheet. Therefore, erroneous detection of the edge of the original paper sheet may occur. As a result, size detection of an original paper sheet based on a result of the edge detection of the original paper sheet may include errors.
In other words, only using intensity variation of received light, it may be difficult to correctly determine whether the received light is light reflected by an original paper sheet or the paper pressing sheet, or other disturbance light.
Further, images present in the original paper sheet may be erroneously detected as the edge of the paper sheet. Thereby, detection of the edge of original paper sheet may be confused in the apparatus. In order to prevent such a problem due to the contents of the images present in the original paper sheet, a diameter of the scanning light spot may be a relatively larger one. It is possible to have a relatively larger beam-spot diameter. However, it is advantageous to instead use a light-emitting diode. In fact, when using laser light in a public-use apparatus, it is necessary to provide many safety devices so as to fulfill many safety regulations. Further, it is likely that a system using laser light is adversely affected by electric noise, driving of the system is relatively difficult, and the system is relatively costly.
A case may be considered in which a light-emitting diode is combined with the above-mentioned hologram in the information reading apparatus disclosed in the Japanese Patent Publication No.59-22992. However, in this case, light passing through the hologram may have a very long sectional shape due to diffusion occurring when an optical path is long. Thereby, resolution may be too low to perform an effective function. Thus, it may be difficult to apply a light-emitting diode, which is easy to handle, in the disclosed method.
In the above-described light-scanning original reading apparatus disclosed in Japanese Laid-Open Patent Application No.6-242391, light from the light source is used to scan the surface of the original paper sheet. Using an intensity of light reflected, it is distinguished whether the light is reflected by the paper sheet or by another surface. However, various images may be present on the original paper sheet, as mentioned above. As a result, there is a possibility that a sharp variation in light intensity occurring when the light scans an image present on the original paper sheet is erroneously recognized to be a sharp variation in light intensity occurring when the light scans an edge of the paper sheet.
Further, the above-described optical reading apparatus disclosed-in the Japanese Laid-Open Patent Application No.50-119537 uses laser light. Therefore, as described above, it is necessary to provide many safety devices, it is likely that a system using laser light is adversely affected by electric noise, and driving of the system costs much.
An optical sensor such as that mentioned above is used to detect a size and/or a position of an original paper sheet of a copying machine, for recognizing information provided on articles such as bar codes, for detecting articles in a factory, and so forth.
For example, the above-described light-scanning original reading apparatus disclosed in the Japanese Laid-Open Patent Application No.6-242391 uses an optical sensor using a semiconductor laser for producing a laser beam in the above-mentioned light scanning means in an optical sensor.
Further, the Japanese Patent Publication No.53-42576 discloses an optical reading apparatus using an optical sensor in which laser light emitted by a laser oscillator is caused to pass through a center of a mirror having an opening. Then, the light is used to scan a to-be-read part through a plurality of deflection mirrors. Then, light reflected by the to-be-read part and passing a path the same as a path which the light passed when it was used for the scanning is reflected by a rear surface of the mirror having the opening. The light reflected by the rear surface of the mirror having the opening is received by a photoelectric converter and converted into an electric signal. Thus, information of the to-be-read part is read.
As described above, laser light is used to scan a to-be-detected object in each of the above-mentioned optical sensors. A reason for using laser light is to reduce a spot diameter formed on a to-be-detected object. However, as mentioned above, in order to use laser light in a public-use apparatus, it is necessary to provide many safety devices for fulfilling many safety regulations. As a result, the apparatus is costly and has a large size.
In order to eliminate such problems, a laser light source in a light scanning system in the related art can be replaced with a point-light-source light-emitting diode having a diameter of a light-emitting area not longer than 0.05 mm for obtaining an appropriate scanning-beam diameter. However, there are few manufacturers which provide such point-light-source light-emitting diodes, and such point-light-source light-emitting diodes are costly in comparison to ordinary light-emitting diodes. Further, because frequencies which can be used in such point-light-source light-emitting diodes are limited, it is not possible to actually use them for the above-mentioned purpose. Because each of ordinary, non-expensive light-emitting diodes on the market has a large light-emitting area of 0.3 mm, it is not possible to replace the laser light source in the light scanning system in the related art with a light-emitting diode.